The present invention relates to plasma panels more particularly plasma panels of the coplanar type.
Plasma panels (called PDP) are image display screens of the flat-screen type. There are two broad groups of PDP, namely PDPs whose function is of the DC type and those whose function is of the AC type. All these PDPs operate on the principle of a gas discharge accompanied by light emission. They generally comprise two insulating tiles each carrying one or more arrays of electrodes and defining between them a space filled with gas. The tiles are joined together so that the arrays of electrodes are orthogonal. Each electrode intersection defines a cell to which a gas space corresponds.
Among plasma panels of the AC operation type, two panel structures are currently used, namely so-called matrix structures, in which the sustaining discharges and the addressing discharges take place between an array of electrodes on the front substrate and an array of electrodes on the rear substrate, and so-called coplanar structures, in which the sustaining discharges are produced between two parallel arrays of electrodes deposited on the front substrate and the addressing discharges take place between one of the arrays of electrodes on the front substrate and the array of electrodes on the rear substrate.
The present invention relates more particularly to the latter type of structure.
More specifically and as shown in FIG. 1, coplanar-type plasma panels currently manufactured firstly comprise a rear substrate 1 consisting of a glass tile. In the embodiment shown, an addressing or column array of electrodes 2 is produced on this glass tile. This array of electrodes 2 is possibly covered with a dielectric layer 3, this layer being necessary for AC operation. Next, barriers 4 are deposited on this layer 3, these barriers being described in greater detail below. The plasma panel shown in FIG. 1 also includes a front element consisting of a front tile 5 made of glass. An array of two parallel electrodes 6 and 6xe2x80x2, forming the sustaining electrodes, has been deposited on this tile. In order for the display to have good viewing characteristics, these electrodes are made of a transparent material such as indium tin oxide, called ITO. However, since the transparent materials used for the sustaining electrodes 6, 6xe2x80x2 have a low conductivity, an electrode-bus 7, 7xe2x80x2, made of a metallic material such as aluminium or silver, or a chromium-copper-chromium coating is also deposited on each of these electrodes 6 or 6xe2x80x2. As shown in FIG. 1, a dielectric layer 8, usually made of a lead borosilicate glass frit, is deposited on the sustaining electrodes 6, 6xe2x80x2. This layer 8 is covered with a protective layer 9, generally made of magnesium oxide (MgO). In this type of panel, the barriers 4 are always of the xe2x80x9csupportingxe2x80x9d type, that is to say their height h corresponds to the distance separating the rear element from the front element of the panel. These barriers have the shape of walls with a width l of between 40 and 100 xcexcm and their height h is between 120 and 200 xcexcm. Since these barriers are of the xe2x80x9csupportingxe2x80x9d type, they must be uniform in heightxe2x80x94their height cannot vary by more than at most +/xe2x88x923%. This is because too great a height variation xcex94h means that there is a space xcex94h between the top of a barrier and the front substrate. This space may be sufficient to allow extension of the discharge from one cell into its neighbour by charge transfer. This phenomenon is detrimental to the operation of the panel. Indeed, the existence of a channel formed by this space allows charge diffusion between adjacent cells, one of which may be ignited while the other is extinguished. This charge diffusion then causes unintentional ignition of the so-called extinguished cell. Moreover, the barriers are always deposited on the rear substrate 1 because the sustaining discharges are produced at the surface of the front substrate. Now, these barriers define a cup, an arrangement which allows the phosphors Ip to be received, and these phosphors must not be in contact with the discharge in order to prevent their degradation.
The object of the present invention is to propose a novel plasma panel structure of the coplanar type, allowing the various drawbacks mentioned above to be overcome.
The subject of the present invention is therefore a plasma panel comprising a first tile called the rear tile and a second tile called the front tile, the two tiles being joined together with a distance of separation defining a space filled with gas, a first array of electrodes which is formed from a set of two parallel electrodes, called the sustaining electrodes, which are positioned on one of the tiles, a second array of electrodes, called the addressing electrodes, which are placed on the other tile perpendicular to the first array, and an array of barriers which is placed on one of the tiles parallel to the array of addressing electrodes, characterized in that the array of barriers is positioned on the tile carrying the first array of electrodes.
According to another characteristic of the present invention, the barriers have a height of less than the distance of separation between the two tiles, the separation between the two tiles being obtained by specific spacing means.
However, the present invention may also apply to panels having full-height barriers.
According to a preferred embodiment, the array of barriers is placed on the rear tile and the height of the barriers is between 60 and 80% of the distance of separation between the tiles.
According to another characteristic of the present invention, a first array of phosphors is deposited on the front tile and a second array of phosphors is deposited on the rear tile in regions not subjected to discharges. The purpose of this second array of phosphors is to increase the area covered by phosphors and therefore the light output of the panel. The second array of phosphors is preferably deposited on the side wall of the barriers.
In this case and according to an additional characteristic of the present invention, the spacing means consists of balls or studs, the balls or studs being positioned either on the front tile or on the rear tile.
The present invention also relates to a rear element for a plasma panel characterized in that it comprises:
a tile;
a first array of sustaining electrodes which is deposited on the tile;
a layer of a so-called thick dielectric material;
a layer for protection against ion bombardment due to the discharge;
an array of barriers.
According to a preferred embodiment, the array of sustaining electrodes is produced by photoetching thin metal layers or by screen printing a conductive paste, such as a silver paste. In addition, the dielectric layer consists of a paste containing a glass frit such as a lead borosilicate and the protective layer consists of a layer of magnesia.
According to another characteristic of the present invention, the rear element also includes an array of phosphors which is deposited in the regions not subjected to discharges.
The present invention also relates to a front element for a plasma panel, characterized in that it comprises:
a tile;
an array of addressing electrodes;
a layer of an insulating material; and
an array of phosphors.
According to a preferred embodiment, the array of addressing electrodes is produced by photoetching a transparent conductive layer, and the insulating material consists of a glass frit, such as a lead borosilicate, or of silica, alumina or magnesium oxide deposited as thin films. Moreover, the front element includes, between the array of addressing electrodes and the layer of insulating material, a black matrix deposited in the low-emissivity regions of the surface in order to reduce the diffuse reflection coefficient of the panel.